Always has trouble with NOX too high. Have tried multiple de-carbonizing additives in the fuel. Brand new O2 sensors, brand new complete exhaust system including cats, new spark plugs, fresh oil, new ignition coils. From what I have read this was the first year for the HE heads, designed to run more on the lean side to improve mileage and pass California emissions laws, since California is a big market for these cars. There must be some component or trick to make this car run a little richer.
Any info on this?